1. Field of the Invention
The present invention relates to an apparatus and method for the continuous growth of a silicon sheet crystal for use in the manufacture of microchips in computer circuits, solar cells, or other devices.
2. Description of the Prior Art
The general method used for forming a silicon sheet crystal is to melt a source of silicon in a crucible and to draw the sheet of silicon from the molten source, which is cooled and solidified. For the sheet growth to be rapid, the solid-liquid interface must be of a substantially greater area than the cross-section of the sheet. The heat of fusion is liberated over a large area and can readily be removed by radiation, convection or conduction. Currently available fast, sheet growth methods include growth by horizontal ribbon growth or low, angle silicon sheet growth. These methods consist of holding the silicon melt in a quartz crucible and growing the ribbon laterally (within about 10.degree. of horizontal) from the melt surface. Passive thermal modifiers, such as scrapers and inert gas cold shoes are used in an attempt to control the thermal environment of the sheet. The difficulty with these techniques is that a dendritic growth morphology degrades the ribbon quality, resulting in considerable waste.
Other fast, sheet growth methods include spin-casting the liquid on rapidly rotating horizontal disc or cylindrical wheel surfaces. None of these methods have been found entirely satisfactory for the creation of a uniform silicon sheet crystal that can be used as a substrate for computer chips or solar cells.